Artificial dielectric material for use in microwave optics



EXAMiNE:

5/ 9 Mr Feb. 25, 1969 w. M. LIGHTBOWNE 3, 3 8

ARTIFICIAL DIELECTRIC MATERIAL FOR USE IN MICROWAVE OPTICS Sheet of 2Filed Jan.

a m mm h N 0. W M ma 2 M J Y B ARTIFICIAL DIELECTRIC MATERIAL FOR USE INMICROWAVE OPTICS Filed Jan. 6, 1966 Feb. 25, 1969 w. M. LIGHTBOWNE FIG.4

William M.L|ghtbowne,

INVENTOR. M m. BY (AM! J. M )W M M e. M

United States Patent ()1 lice 8 Claims Int. Cl. H011] 15/08 ABSTRACT OFTHE DISCLOSURE An artificial dielectric material wherein an array ofdiscrete dipoles formed by wraping cylinders of foil around plastic rodsis interspersed and oriented in a three-dimensional repeating pattern,identical in the three principal planes, and supported by a lattice ofinsulating material.

This invention relates to artificial dielectric materials whoserefractive index is precisely controlled by the physical dimensions ofits component parts and which exhibits superior properties in respect tobandwidth, isotropy, power factor, ruggedness, stability, cost andavailability.

Prior art dielectrics for the higher frequencies have been developed inwhich small metal strips, flakes or platelets are dispersed by variousmeans throughout the mass of a foamed natural dielectric-usuallypolystyrene. This type of material, known as loaded foam, is the onlyknown method of augmenting the refractive properties of naturaldielectrics. It is heavy, expensive, lossy, and non-uniform in texture.For the lower frequencies, in the VHF and UHF bands, satisfactorymaterials have been developed, however, these materials have not beenfound suitable for production.

The present invention overcomes the disadvantages of the prior artmaterials and consists of (1) an array of discrete dipoles, interspersedand oriented in a three dimensional repeating pattern of cubic cells,having identical aspects in the three principle planes; and (2) asupporting lattice. Inasmuch as the dipoles are physicallydiscontinuous, the supporting lattice must provide all the desiredstructural properties of the material. Furthermore, since the supportinglattice is part of the propagating medium, it must also possesscompatible electrical properties.

It is an object of the present invention to provide an artificialdielectric possessing sufficient isotropy for use in the fields of radarand microwave optics.

Another object of this invention is to provide an artificial dielectricthat can be economically produced in large quantities.

These and other objects and advantages of the invention will becomereadily apparent upon an inspection of the following detaileddescription and the accompanying drawing in which:

FIGURE 1 is an illustration of the structure of a dipole memberaccording to the invention;

FIGURE 2 is an illustration of an alternate form of the dipole member;

FIGURE 3 is a perspective view of supporting lattice according to afirst embodiment of the invention; and

FIGURE 4 is a perspective view of a second embodiment of the invention.

Referring now to FIGURE 1, dipole member is shown to consist ofcylinders of foil or sheet metal 12 wrapped around plastic rod 14. Rods14 are cut to about one wavelength at the desired center frequency. Tominimize anisotropy and frequency dispersion, there should be abouttwelve dipoles per wavelength.

3,430,248 Patented Feb. 25, 1969 An alternate form of the dipole member10 is shown in FIGURE 2. This form is obtained by taking a long flatstrip of plastic 16 and cementing metal foil elements 18 thereon. Thisstrip is then curled into long tubes.

The supporting lattice consists of a cube 20 whose side is the samelength as rod 14 which bears the dipoles. Cube 20 is composed ofexpanded polystyrene foam and has groups of holes 22, 24, and 26 moldedor drilled therein normal to each face of the cube. The holes in eachface are equally spaced and the number of holes is equal to the squareof the number of dipoles on a rod 14. The holes have a diameterapproximately equal to that of dipole member 10.

The diameter of dipole member 10 shall be such that when holes 22, 24,and 26 are formed in cube 20 from three mutually perpendicular faces ofthe cube, no two holes shall intersect, and the clearance between allholes passing tangent to one another shall be approximately equal.

A second embodiment of the invention is shown in FIGURE 4 and differsfrom that of FIGURE 1 mainly in that the cube is formed from a pluralityof square polystyrene tubes. In FIGURE 4, the dipoles 31 are discretestrips, crosses, 0r squares of foil or sheet metal which have beencemented to, in a regular pattern, large sheets of thin insulatingmaterial. The insulation material should be dimensionally stable,mechanically strong, and have the electrical properties of extremely lowloss and low dielectric constant at the desired operating frequency. Oneexample of such a material is biaxially-oriented extruded polystyrenesheet.

These sheets, with their laminated patterns, are carefully cut intorectangles. The rectangles are then folded or formed into long tubes,which may be square, octagonal, or circular in cross-section. The foldsare so positioned with respect to the dipole pattern that the resultingtube is symmetrical about two principal planes, whose intersection isthe axis of the tube, and which pass either normal to the sides ordiagonally through the corners, of the tube. Metal dipoles 31 may belocated either on the inside or the outside surface of tubes 32, 34, and36. The length of the tubes must be uniform and each should contain aneven number of dipole patterns. A preferred length, as in FIGURE 1,would be one wavelength with twelve sets of dipoles along eachc side ofa tube. In crosssection, the side of the tube should precisely equal thespacing of the dipole patterns.

With these dimensions established, a number of these tubes 32, 34, and36 can be constructed in the longitudinal, lateral and vertical axes asshown in FIGURE 4 to form cube 30. The addition of a cement or solventat each interface creates a rigid, continuous, cubic lattice whichpossesses a characteristic mechanical symmetry.

It can be seen from the above that any dipole arrangement, in accordwith the above described embodiments, provides a cell of dipoles inthree dimensions, at the intersection of each tube with any other tubeor with any tube in an adjacent block similarly oriented. This cell willalso possess triaxial symmetry which provides the dielectric withsufficient isotropy for many applications of microwave optics.Specifically, the artificial dielectric described herein is suitable"for use in Luneberg Lens receiver antennas. It should also be notedthat any desired refractive index can be obtained in any of theembodiments of the invention simply by adjusting the physical dimensionsof the dipole array, the dipoles, or both.

While this invention has been described with reference to particularembodiments thereof, the following claims are intended to include thosemodifications and variations that are within the spirit and scope of myinvention.

I claim:

1. An artificial dielectric material comprising an array of discretedipoles interspersed and oriented in a three dimensional repeatingpattern having identical aspects in the three principal planes, and asupporting lattice of insulating material for supporting said poles insaid pattern.

2. An artificial dielectric material comprising: a cube of expandedplastic material, said cube having holes formed therein from threemutually perpendicular faces, and dipole members disposed in said holesand formed of alternate sections of dipoles and insulators, said dipolemembers having a length equal to a side dimension of said cube.

3. An artificial dielectric material as set forth in claim 2 wherein thenumber of holes formed in each face of said cube is equal to the squareof the number of dipoles in a dipole member.

4. An artificial dielectric material as set forth in claim 2 whereinsaid dipole member is in the form of a rod of insulating material havingbands of metal wrapped therearound at spaced positions along the lengththereof.

5. An artificial dielectric material as set forth in claim 2 whereinsaid dipole member is in the form of long flat sheet of plastic materialto which metal elements have been cemented and said sheet has beencurled to form :1 tube.

6. An artificial dielectric material comprising a cubical body ofinsulating material and a plurality of dipoles distributed uniformlythroughout said body, said body being formed of a plurality of discretetubular insulating members disposed along three mutually perpendicularaxes in a lattice configuration.

7. An artificial dielectric material as set forth in claim 6 whereinsaid tubular members are formed of rectangular sheets of insulatingmaterial having said dipoles cemented thereto in a regular pattern andfolded so as to form a tube that is symmetrical about two principalplanes, intersecting at the axis of the tube.

8. An artificial dielectric material as set forth in claim 2 whereinsaid expanded plastic is polystyrene foam.

References Cited UNITED STATES PATENTS 2,579,324 12/1951 Kock 343-9112,936,453 5/1960 Coleman 343-915 3,165,750 1/1965 Tell 343-911 3,254,3455/1966 Hannan 343-911 3,293,649 12/1966 Fox et al. 343-911 FOREIGNPATENTS 665,747 1/1952 Great Britain.

ELI LIEBERMAN, Primary Examiner.

